Tuesday, September 8, 2009

For reasons that are not to hard to fathom, myths about chameleons abound. The Victorians thought they lived entirely on air; a common Zulu superstition is that they're evil (as I confirmed for myself a while back when I tried to show a chameleon I had caught to our gardener); and, more recently, I've been hearing a lot of people say chameleon color changing has nothing to do with camouflage. Even Cracked has got in on the act with an article on "bullshit animals facts", which argues a chameleon's color is determined largely by its mood. I call bullshit on their bullshit.

Thanks to frequent childhood visits to a family farm, I've had lots of encounters with these amazing critters and I've seen them change color to blend in with their environment with my own eyes. Not particularly good evidence, I hear you say. Agreed, so I spent 2 minutes on Wikipedia, followed a link, and found thisNew Scientist piece, about this study in Biology Letters. And guess what? At least one species of chameleon, Smith's dwarf chameleon (which, incidentally, is South African), does change color to camouflage itself from predators. The paper, "Predator-specific camouflage in chameleons" by Stuart-Fox et. al., demonstrated in several behavioral trials that these chameleons engage in background matching when presented with model predators. In other words, these guys do their best to blend in with their environment when they encounter things that want to eat them. (You can see a clear example of a chameleon matching its background in this YouTube clip [Note: James informs me in the comments that this might be fake]).

So why do people think chameleon camouflage is a myth? It seems other research (also by Stuart-Fox) that concluded color changing evolved for social signalling has been misinterpreted. The conclusion of this second paper was: "our results suggest that selection for conspicuous social signals drives the evolution of colour change in this system, supporting the view that transitory display traits should be under strong selection for signal detectability." In other words, the primary evolutionary 'function' of color changing in chameleons seems to be social signalling. But it does not follow from this that chameleons cannot also use color changing for crypsis -- the ability may have evolved for social signalling, but nothing stops it from being exapted for camouflage. It is such an obvious evolutionary trick that I'm surprised anyone interpreted Stuart-Fox et. al. second paper in this way. If you already have a visual system (to detect background color), you can already change color, you suffer predation and camouflage thus increases fitness, we should positively expect exaptation for crypsis.

As I also pointed out on my fox domistication piece, I'm not a biologist so you should be especially skeptical of my opinions on this (though, I managed to convince biologist Richard Glor over at Dechronization that my interpretation is right). But still... At least some chameleons change their color to blend in with their environment. Obviously.

UPDATE: I emailed Stuart-Fox and asked whether my take is correct. Here is the reply in part (my emphasis):

Yes, your interpretation is correct. Colour change in chameleons serves multiple current functions including camouflage (background matching), thermoregulation and communication (courtship and male-male contests). But we need to distinguish current functions from the selective pressures driving the evolution of the abiltiy to change colours. Some species can change colours much more than others - the question I was trying to answer is why such variation? And it seems that sexual selection for communication (signalling) is the most important selective pressure because the species that change colour the most have the most conspicuous colour patterns that they use to communicate.

I am extremely suspicious of YouTube videos because it is easy to generate such an effect via editing software. But the real reason I think it is faked is because, as you mentioned above, certain species have been observed to match the environment (not necessarily all species can) but the chameleon appear very relaxed and unperturbed by having to walk over glasses. My question is; where is the predator threat to induce colour changing? I imagine that if a real biologist who studies chameleons were to weigh-in with an opinion it would be that the video has too many questions to be taken on face value. If it felt it should camouflage, why was it not desk-coloured at the start?

Of course, the possibility is that females show a preference for the males who can blend in best to their environment, or even that the males use that ability to fertilise them without giving the female much choice (no one ever said the natural world was nice). That would link sexual and natural selection quite nicely in a reinforcing loop which would eventually result in ghostly lizards that can walk through solid walls. I don't have any data that that is in fact the case, though.

"or even that the males use that ability to fertilise them without giving the female much choice (no one ever said the natural world was nice)". Well, you're right about the natural world not being nice, but it also means that there already exists much simpler ways to "not give the female much choice" than evolve a really complicated camouflage system. And I fail to see (no pun intended) why the female couldn't use other clues to detect the presence of male that close to her. And it's not like they are really fast running creatures... And I'm not a specialist of chameleons, so I don't know much about their visual system, but maybe they don't share it with their most common predators, in which case it would be kinda useless. Furthermore, if the cryptic nature of males impacted the females reproductive capacity, we would expect them to develop a counter adaptation.

That video is fake, veiled chameleons cannot change color like that. And chameleons don't change color to blend in with their surroundings. Yes most wild chameleon's natural color is the color of their natural surroundings, but if you take a chameleon and put it in front of a bright pink, blue or whatever color wall it will not and cannot change into that color. Chameleons change color based on mood and temperature, or flare up to brighter colors to attract a mate, or scare off other chameleons.

When he was an innocent undergrad Michael studied Politics, Philosophy & Economics at the University of Cape Town. Unfortunately, he had to find out for himself that "social" and "science" often don't go so well together.